This invention relates to compound archery bows and, in particular, to wheels capable of being laced at least three ways.
Compound bows differ from long bows in that a block and tackle mechanism is used to bend the bow: wheels are attached at the free ends of the limbs and lacing is wound around the wheels and attached to the limbs to obtain a mechanical advantage in bending the bow. The wheels and lacing differ from a block and tackle mechanism in that the wheels of a compound bow are eccentrically mounted on axles, causing a substantial "let off" or reduction in the holding force of a drawn bow, an effect more closely resembling that of levers rotating about the ends of the limbs of the bow.
As used herein, "wheel" refers to the entire rotating member at the end of a limb of a compound bow. The wheel is machined from metal, preferably aluminum or aluminum alloy, rigid plastic, or other rigid material. A wheel appears to be two adjoining disks having grooved rims, herein referred to as "pulleys," mounted on a common axle. In some compound bows, each wheel is actually two separate pulleys fastened together.
Compound bows typically use two wheels, with lacing wound from an anchor at one end of a one limb to the wheel at the end of the other limb, to the wheel at the end of the one limb, then back to an anchor on the other limb. As used herein, "lacing" can refer to a one piece bowstring or a three piece line comprising two end cables connected by a central stretch between the wheels which forms the bowstring. The lacing can be made from a variety of materials, i.e. the words "cable" and "string" imply location rather than material. A bowstring is typically a high strength man-made polymer fiber, such as high tensile strength polyester. The cables are either metal wires or polymer fibers.
For the manufacturer, there is a problem in how the lacing is attached to the wheels. Over the years, three basic techniques have developed for fastening the lacing to the wheels, each requiring a different wheel.
One type of lacing uses two metal cables, each terminating in what is known as a teardrop connector. The bowstring is shorter than the span between the wheels and has a closed loop formed at each end. The loops go over the teardrop connector at the free ends of each cable. Each cable extends from the teardrop connector and winds almost all of the way around the string pulley at the end of one limb, passes through the wheel to the cable side of the wheel and winds part way around the cable pulley, then extends to an anchor on the other limb. A setscrew in the wheel crimps the cable at some point to keep the cable from sliding around the pulley. A variation on this type of lacing uses no teardrop connectors and a one piece lacing.
A second type of lacing eliminates the teardrop connector and uses a bowstring which is longer than the span between the wheels. A closed loop is formed at each end of the bowstring. At one end, the loop engages a post in the interior of the wheel and the bowstring passes through an opening in the rim of the string pulley to wind almost all of the way around the string pulley, then across the span to similarly engage the other string pulley. The string pulley may have several openings spaced around its rim for changing the draw length of the bow, depending upon which opening is used. Each cable has a ferrule bonded to one end which fits in a socket in the interior of the cable side of the wheel. From the socket, the cable exits through an opening in the rim of the cable pulley, winds part way around the cable pulley, and extends to an anchor on the other limb.
In the third type of lacing, the bowstring is the same as in the second type of lacing. The cable is a polymer fiber, often the same material as the bowstring, and has a closed loop formed in one end instead of having a ferrule. The loop goes over a post on the cable side of the wheel and the cable exits through an opening in the rim of the cable pulley, winds part way around the cable pulley, and extends to an anchor on the other limb. For all three types of lacing, the bowstring and cable are wound on a wheel so that, as the bow is drawn, the bowstring unwinds and the cable winds further.
Each of the three types of lacing has its advantages and disadvantages, proponents and opponents. A wheel adapted to one type of lacing is typically incompatible with other types of lacing. One cannot arbitrarily add posts or sockets to the first type of wheel in order to adapt the wheel to other types of lacing since this may weaken the wheel, which must bear large forces especially when the bow is fired.
There are also three basic types of pulleys in terms of performance. Each pulley in a wheel can be either cam shaped or round. A cam shaped pulley produces a higher performance bow than a round pulley. By performance is meant the amount of energy stored in a drawn bow. In general, a higher performance bow is harder to draw, hence the greater energy stored, and requires more careful tuning, i.e. more careful adjustment of the bow to the size and style of the archer.
There are a large number of combinations of lacing and shapes for a wheel. When further combined with the variations in limb stiffness, handle geometry, arrow rest, and sight, the manufacturer is faced with an ever growing matrix of variables in order to accommodate the needs and preferences of its customers. The retailer is faced with a corresponding problem in stocking all the components and various pre-assembled bows from the manufacturer. While the variety benefits the customer, it is very costly for the manufacturer and retailer.
In the prior art, U.S. Pat. No. 4,078,538 discloses the first type of lacing but uses a mount clip instead of a setscrew for attaching the cable to the wheel. U.S. Pat. No. 4,241,715 discloses the first type of lacing and discloses anchoring the cable to the wheel rather than the limb. U.S. Pat. No. 4,739,744 discloses wheels having separate pulleys. U.S. Pat. No. 4,957,094 discloses the third type of lacing, i.e. both the cables and the bowstring attach to the wheel with loops.
In view of the foregoing, it is an object of the invention to provide a wheel for a compound bow which can accommodate all three types of lacing.
Another object of the invention is to provide three way connections on a wheel for a compound bow without weakening the wheel.
A further object of the invention is to provide a three way post connector for a wheel in a compound bow.